I received a correction by email on the 十 kanji page on TJP.com.  We had had the following example sentence:

 私は十歳です。
watashi wa juusai desu.
I am 10 years old.

 They correctly corrected me by saying it should be jissai instead of juusai.

I knew radio and tv announcers say 「じっさい」 but I wasn't aware 「じゅうさい」 was incorrect.  Turns out there is no little discussion on this in Japanese forums and blogs.  Most people say 「じゅっさい」 with a small っ or 「じっさい」 but not 「じゅうさい」. 

Well, I know I should have learned this from the first few pages of my first textbook on Japanese, but I guess that is the page my dog ate.

So you can say:

実際に「じっさい」が正しいけれど、「じゅっさい」は実際によく使われている。
jissai ni jissai ga tadashii keredo, jussai wa jissai ni yoku tsukawareteiru.
Really, 'jissai' is correct, but 'jussai' is really often used.